Hydrocarbyl succinimides, such as those derived from polyalkylene polyamines, are known materials which have been widely used as fuel detergents. For example, U.S. Pat. No. 4,240,803 describes the use of alkenyl succinimides in gasoline to reduce engine deposits. Also, U.S. Pat. No. 4,482,357 discloses additive mixtures for diesel fuels which include a hydrocarbyl succinimide or succinamide and the reduction of coke deposition by the use of these additive mixtures.
Additives are an important means of maintaining engine performance either by cleaning and/or lubricating moving parts of the engine. It is well known in the art to prepare hydrocarbyl substituted succinylating agents, and specifically polyisobutenyl succinic anhydrides (PIBSAs) by the reaction of a polyisobutene with maleic anhydride and to convert the PIBSAs to the corresponding succinimides by reaction with a polyethylene polyamine as described in U.S. Pat. No. 5,644,001. These succinimides are used as fuel additives for their ability to clean and/or maintain in a clean condition carburetors, manifolds, inlet valve ports, fuel injectors and the like in an internal combustion engine.
The polyisobutenyl succinic anhydride intermediate may be produced following two main processes. The first process consists of a direct thermal condensation reaction between maleic anhydride and polybutene and is often referred in the art as the thermal ene reaction. Elevated temperatures above 200° C. are required to obtain good reaction yields. These high temperatures lead to the formation of resin (sediment) which is believed to be due to the polymerization and/or decomposition of maleic anhydride. The formation of those insoluble resin or sediment in significant amounts requires a filtration stage before the PIBSA can be used as an additive or as an intermediate in the preparation of other products, e.g. succinimides for instance. Furthermore, according to U.S. Pat. No. 5,644,001, those undesirable resin, induce not only a significant discrepancy between the real and apparent succinylation in the maleinised product (due to the presence of resinified and/or unreacted maleic anhydride) but also adversely affect the detergency properties of such additives.
In the second type of process, the chlorination of the polybutene is first carried out, followed by the condensation of the chlorinated polybutene with maleic anhydride. This process can be carried out at lower temperature, than the thermal ene reaction process, with high yield and without the formation of substantial amounts of sediment. However, the polyisobutenyl succinic anhydride obtained with this process contains residual chlorine and environmental concerns related to chlorine-containing materials and potential formation of hazardous products, such as dioxins, that may arise under the conditions prevalent in an internal combustion engine, make the use of the second process undesirable. Furthermore, chlorine is also known to be a poison for the catalysts used for exhaust gas after treatment systems, i.e. as in catalytic converters.
As mentioned in the discussion above, the production of thermal PIBSAs and the corresponding succinimides normally results in resin and various other side products. Removing the resin and other side products require a filtration step, generally performed on pressure filters, e.g. Schenk-type filters, using a filter aid. Furthermore, the viscosity of PIBSAs and the corresponding succinimides makes this filtration step industrially difficult. Thus, prior dilution generally with mineral oil is generally performed to increase the filtration rate. After filtration, the resin saturated filter cake is disposed. However, a significant amount of desired product remains adsorbed on the filter cake as well and therefore results in reduced yield of the product.
As a consequence, there have been important development efforts made to reduce the amount of sediment formed during the ene process. The nature of the polyalkene plays a key role in the efficiency of the ene reaction and the amount of sediment formed during the reaction. Polybutene having a high concentration of terminal vinylidene bonds (greater than 50 wt %) are more reactive and leads to higher conversion and lower sediment. Those polybutenes, also called “reactive polybutene” have been achieved by BF3-catalyzed polymerization of isobutylene. Conventional polybutenes, formed by cationic polymerization using aluminium chloride catalyst have a relatively low content of terminal double bonds (less than 20 wt %).
U.S. Pat. No. 5,071,919 discloses a process for preparing substituted succinic acylating agents by reacting an acidic reactant such as maleic anhydride with a substantially aliphatic polymer comprised principally or entirely of polyisobutenes in a mole ratio of acidic reactant:polymer of at least 1:1, provided that at least 50% of the polyisobutene content of the polymer has terminal vinylidene end groups and the reaction is maintained under super-atmospheric pressure during at least a substantial portion of the reaction period. The patent discloses that reaction product mixtures formed by this process contain little or no tars.
U.S. Pat. No. 5,229,022 which discloses the thermal ene reaction of ethylene-α-olefin polymers having a high terminal ethenylidene (i.e., vinylidene) content with monounsaturated carboxylic reactants in the presence of a catalyst system comprising at least one metallocene and an alumoxane compound. The patent discloses that the ethylene-α-olefin polymers readily undergo thermal ene reactions under conditions in which the formation of sediment or other byproducts contributing to product haze is greatly minimized or avoided altogether. It is further disclosed that the resulting ene reaction product mixture can be employed, without filtering, centrifuging, clarification, phase separation or other conventional product purification treatments.
U.S. Pat. No. 5,739,355 discloses a process for production of an alkenyl anhydride or polyalkenylsuccinic anhydride without forming resin by an ene-synthesis reaction between an olefin or a polyolefin, particularly polyisobutenes that have a content of external double bonds of more than 50%, and maleic anhydride in an aromatic solvent that is selected from toluene and xylenes.
Reagents have also been employed in the thermal ene reaction in order to reduce the formation of tars and sediment. It has been shown that the addition of a strong acid (such as sulfonic acid) to the process of preparing a polyalkenyl derivative of an unsaturated acidic reagent results in a faster rate of reaction, higher conversion, less sediment, and a lower succinic ratio.
U.S. Pat. No. 5,777,025 discloses a process for preparing polyalkenyl derivatives of monosaturated C4 to C10 dicarboxylic acid compounds containing insignificant amounts of sediment by reacting the dicarboxylic acid producing compound with a polyalkylene at high temperature and under high inert gas partial pressure above 2 atmospheres in the presence of a sediment-inhibiting amount of hydrocarbyl substituted sulfonic acid.
U.S. Pat. No. 6,156,850 discloses a process of reacting a polyalkene having a Mn of at least 300 with an unsaturated acidic reagent at elevated temperatures in the absence of a strong acid until at least 25% of the polyalkene is converted to a polyalkenyl derivative of an unsaturated acidic reagent, continuing the reaction of the polyalkene with an excess of the unsaturated acidic reagent at elevated temperatures in the presence of a strong acid to convert at least some of the unreacted polyalkene to additional polyalkenyl derivative of an unsaturated acidic reagent, and removing the unreacted unsaturated acidic reagent. The process may be conducted at atmospheric, sub-atmospheric or super-atmospheric. Preferably, the pressure is super-atmospheric. There is no disclosure in the patent that the process results in a product having low sediment, particularly a sediment level less than 0.1 wt %.